The process of heat staking is a known technique for securing articles in assembled relation. It has found widespread application for joining together plastic molded articles, and also in joining plastic molded articles to a metal article. Broadly, the process has used a formable projection on one article that is brought into registration with an aperture formed in another article to form the assembly. The projection is generally heat softened and staked into a headed shape by action of a forming staking anvil.
In the process of assembling devices, such as computer keyboards and similar items, plastic parts are often locked in place against a metal pan. The pan is apertured to receive a heat formable shank having a portion thereof projecting through the aperture to be melted over to trap the plastic portion against the pan. Conventional heat staking is often done by bringing a heated metal plate in contact with the protruding portion and melting it to form a flanged head extending radially beyond the margin defining the pan aperture. While this appears to be a simple operation, one soon encounters at least two problems. First, some plastics, notably acetol plastics, become gummy and stick to the staking head. Secondly, as the staking head is retracted, it is not unusual for the plastic posts or shanks to still be in the melted state. If not immediately released, the shank will be stretched thereby contracting its diameter and cause the adjoining components of the assembly to be loose with respect to the metal pan. This situation can also occur when a heat staking process is used for joining components to non-metal printed circuit boards or the like.
It is therefore a general object of the present invention to provide a method and apparatus which meet a long standing need in the art of securing components together by means of heat staking.
Specifically, it is an object of this invention to present a method and apparatus which will provide secure connection between adjoining, engaged components and to minimize the possibility of heat deformable plastic post or fastening shank, from sticking to a tool, such as a staking anvil, upon release of the staking anvil from the formed projection or shank.
It is a further object of the present invention to provide a heat staking method and device for joining a first component to a second component, wherein the second component includes a post or shank of heat deformable material having a portion protruding through an aperture in the first component, and further wherein the heat deformable portion will be permitted to tightly secure the components together with minimal shrinkage or contraction of the diameter of the projection or shank portion residing within the aperture.
Another specific object of the present invention is to present a method and apparatus for joining a first and second component together to form a secured assembly, wherein one of the components includes a heat deformable post or shank having a portion thereof projecting through an aperture in the other component, and wherein the protruding portion is heat staked over the margin defining the aperture, and prior to release of a heated staking anvil, the anvil will be chilled to permit a clean withdrawal of the tool from the formed plastic, and thereby minimize the possibility of the plastic projection to be stretched by sticking to the staking head and thereby reduce its diameter within the aperture.
The following United States patents are of interest as background art to the present invention: U.S. Pat. Nos. 2,705,346; 4,633,559 and 4,767,298.